Field of the Invention
The present disclosure relates to control of an image forming apparatus, and more particularly, relates to control of electrophotographic image forming apparatus.
Description of the Related Art
Electrophotographic image forming apparatuses are widely used today. An electrophotographic image forming apparatus performs a printing process that includes a process of forming a toner image on an image carrier such as a photosensitive member or an intermediate transfer member, a process of transferring the toner image from the image carrier onto a paper sheet, and a process of fixing the toner image to the paper sheet.
The transfer of a toner image from an image carrier onto a paper sheet is performed by a transfer member. The transfer member is installed in contact with the image carrier. A voltage of the opposite polarity of that of the toner image (this voltage will be hereinafter also referred to as “transfer voltage”) is applied to the transfer member. With this transfer voltage, the toner image is attracted to the transfer member from the image carrier, and is then transferred onto the paper sheet being conveyed between the image carrier and the transfer member.
The resistance value of the transfer member varies with the surrounding environment or the like. Furthermore, the resistance value of a paper sheet varies with the type of the paper sheet. With such changes, the transfer voltage to be applied to the transfer member might also change, and cause a decrease in print quality. Particularly, unlike the resistance value of plain paper, the resistance value of a paper sheet to be used to achieve special image quality or a special visual or tactile effect (such a paper sheet will be hereinafter also referred to as “special paper”) noticeably reflects a decrease in print quality. To increase the print quality of special paper, the user of the image forming apparatus manually sets an allowable range of change in the transfer voltage for the special paper. In relation to a technology for reducing the load of this setting process, JP 2010-145955 A discloses an image forming apparatus for simplifying the operation to set the transfer voltage for special paper.
When an image carrier and a transfer member are left in an environment where ozone is readily generated or at an ultralow temperature for a long period of time, the resistance values of the image carrier and the transfer member might become higher than expected. As a result, current does not smoothly flow in paper sheets. Furthermore, in a case where printing is performed on a paper sheet with an unexpectedly high resistance value (such as a paper sheet with poor quality), current does not smoothly flow in the paper sheet. In such a case, even if the transfer voltage is finely adjusted, the current flowing in a paper sheet does not greatly change, and therefore, the print quality of the paper sheet does not greatly change, either. In view of this, in the image forming apparatus disclosed in JP 2010-145955 A, the user or maintenance staff needs to set a wide allowable range of transfer voltage change, and conduct test printing repeatedly to achieve desired print quality. In such circumstances, there is a demand for an image forming apparatus in which the magnitude of the current to flow in the paper sheet at the time of printing can be set, instead of the transfer voltage that hardly affects print quality.